In the $^1H\ NMR$ spectrum of an organic compound recorded on a 300 MHz instrument, a proton resonates as a quartet at $\delta\ 4.20\ ppm$. The individual signals of the quartet appear at $\delta\ 4.17,\ 4.19,\ 4.21\ and\ 4.23\ ppm$. The coupling constant J in Hz is ____________.
This question requires calculating the coupling constant ($J$) from the provided $^1H\ NMR$ spectral data.
Calculating the Coupling Constant (J Value)
A quartet signal indicates that the proton is coupled to 3 equivalent neighboring protons.
The individual peaks of the quartet are observed at the following chemical shifts ($\delta$) in ppm:
- $\delta\ 4.17\ ppm$
- $\delta\ 4.19\ ppm$
- $\delta\ 4.21\ ppm$
- $\delta\ 4.23\ ppm$
Determining Peak Spacing
The coupling constant ($J$) is the distance between adjacent peaks in the multiplet, measured in Hertz (Hz). We can first find the spacing in parts per million (ppm) from the data:
- Spacing between the first and second peak: $4.19\ ppm - 4.17\ ppm = 0.02\ ppm$
- Spacing between the second and third peak: $4.21\ ppm - 4.19\ ppm = 0.02\ ppm$
- Spacing between the third and fourth peak: $4.23\ ppm - 4.21\ ppm = 0.02\ ppm$
The consistent spacing between the peaks of the quartet is $0.02\ ppm$.
Converting ppm to Hertz (Hz)
To convert the spacing from ppm to Hz, we use the formula:
$J\ (Hz) = \Delta\delta\ (ppm) \times Spectrometer\ Frequency\ (MHz)$
Given:
- Spacing ($\Delta\delta$) = $0.02\ ppm$
- Spectrometer Frequency = $300\ MHz$
Now, substitute the values into the formula:
$J\ (Hz) = 0.02\ ppm \times 300\ MHz$
$J\ (Hz) = 6\ Hz$
Therefore, the coupling constant ($J$) for this proton is $6\ Hz$.
Important Questions from NMR Spectroscopy (1H and 13C)
In the $^1H$-NMR spectrum of the following molecule, the signal of proton $H_a$ appears as
The $^1H$ NMR spectrum of the given iridium complex at room temperature gave a single signal at 2.6 ppm, and its $^{31}P$ NMR spectrum gave a single signal at 23.0 ppm. When the spectra were recorded at lower temperatures, both these signals split into a complex pattern. The intra-molecular dynamic processes shown by this molecule are
Compound K displayed a strong band at $1680 \text{ cm}^{-1}$ in its IR spectrum. Its $^1H$-NMR spectral data are as follows: $\delta$ (ppm) 7.30 (d, J = 7.2 Hz, 2H), 6.8 (d, J = 7.2 Hz, 2H), 3.8 (septet, J = 7.0 Hz, 1H), 2.2 (s, 3H), 1.9 (d, J = 7.0 Hz, 6H). The correct structure of compound K is
$^1H$ NMR spectrum of a mixture containing $CH_3Br$ ($x$ mol) and $(CH_3)_3CBr$ ($y$ mol) shows two singlets at 2.7 ppm and 1.8 ppm, with the relative ratio of 3:1 (integration value), respectively. The value of $x/y$ is ____________
(rounded off to the nearest integer)Consider the following $^1H$-NMR ($400$ MHz, DMSO-$d_6$) data of a compound:
$\delta$ in ppm: $3.85$ (s, $6H$), $6.73$ (t, $J = 2.2$ Hz, $1H$), $7.1$ (d, $J = 2.2$ Hz, $2H$), and $13.05$ (brs, $1H$).
The compound is
